And the one line answer is:
http://www.mountainviewdata.com/us/technology/snapfs.html
it does depend on having ext3fs or XFS compiled into the kernel, so it'll be
quite happy with either 2.2 or 2.4 kernels respectively.
Cheers,
-Thom
* Peter Rundle ([EMAIL PROTECTED]) wrote on Thu Mar 29, 2001 at 10:58:16
+1000:
> Sluggers,
>
> Does anyone know if there is a Veritas equivilent to doing file
> based snapshots in Linux. I've been told that this is available
> in the Logical Volume Manager (LVM) but looking at their site it
> appears that they do volume based snapshots not file based.
> And these snapshots in fact copy the entire data.
>
> The basic method is like this,
>
> The file system inode points to the blocks that make up the
> file. When a snapshot of the file is made a new inode is
> created which has a duplicate set of pointers to the same
> blocks. (Note I use "inode" here loosely, as I'm not sure that
> it's quite the same as an ext2 inode).
>
> A request to write to a block in the file is met by copying the
> block to a new location and updating the original inode pointer
> to point to the new location but leaving the copied inode alone.
>
> Snapshot initial creation
>
> +---------+
> fileinode +---> | block 0 | <---+ newinode
> | +---------+ |
> |---> | block 1 | <---+
> | +---------+ |
> +---> | block 2 | <---+
> +---------+
>
> After write to block 1 of the file
>
> +---------+
> fileinode +---> | block 0 | <---+ newinode
> | +---------+ |
> | | block 1 | <---+
> | +---------+ |
> +---> | block 2 | <---+
> | +---------+
> +---> | block 1 |
> +---------+
>
> So newinode is a point in time snapshot which I can backup to
> tape at my leisure. The advantage of which is that I don't need
> twice the disk space to make a "point in time copy". Of course
> if I leave the snapshot in place for long enough the file will
> eventually roll through all the pointers so that I in fact have
> two seperate files.
>
> Does anybody know of a Linux equivelent to this?
>
> Thanks
>
> Pete
>
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